Early attempts to suppress organic pain and other neurophysiological effects utilizing electrical signals occurred as early as about 2000 years ago when gout was apparently successfully treated by placing the extremities of a patient in a tub of water filled with Torpedo fish or electric eels. Later headaches were treated using a similar approach. A detailed, scientific investigation was then later conducted by Professor Galvani, professor of anatomy at the University of Bologna, and this is believed to have led to the development, during the 19th century, of electrical equipment for suppression of organic pain.
Among early patent literature, U.S. Pat. Nos. 646,793 (Bentz, issued in 1900), 872,148 (Raymond and Vetter, issued in 1907), 1,059,090 (Tibbals, issued in 1913), 1,305,725 (Kent, issued in 1919), 1,667,451 (Arnberg, issued in 1928), and 1,908,688 (Call, issued in 1933) are all directed to therapeutic devices wherein electricity was utilized as a stimulant.
During the 1950's, U.S. Pat. Nos. 2,622,601 (Nemec, issued in 1952), 2,624,342 (DiPerna, issued in 1953), and 2,771,554 (Gratzl, issued in 1956) were issued directed to electrotherapeutic devices in which the output signals included pulses with at least one of these devices including means to vary the magnitude, rate, and duration of the produced pulses.
With respect to more recently issued patents, U.S. Pat. No. 2,915,066 (Parodi, issued in 1959) is directed to an electro-stimulo-therapy apparatus that utilizes a step-up transformer, U.S. Pat. No. 3,645,267 (Hagfors, issued in 1972) is directed to a nerve stimulator that utilizes an output signal of increasing amplitude, U.S. Pat. No. 3,727,616 (Lenzkes, issued in 1973) is directed to an electronic stimulator that utilizes a CW signal of two frequencies and an implanted receiver, U.S. Pat. No. 3,794,022 (Nawracaj et al, issued in 1974) is directed to an electrotherapeutic device having dual oscillators to apply square wave pulses of increasing duration, U.S. Pat. No. 3,817,252 (Maurer, issued in 1974) is directed to a specific electrode for use in transcutaneous nerve stimulation, U.S. Pat. No. 3,817,254 (Maurer, issued in 1974) is directed to a transcutaneous stimulator in which a series of pulses are produced with each pulse having frequency components substantially ninety percent of the energy of which is specified to fall within substantially 100Hz, to 5,000Hz, and U.S. Pat. No. 3,835,833 (Limoge, issued in 1974) is directed to a method for obtaining neurophysiological effects and utilizes a composite signal.
It has been suggested that electrical impulses arriving at the central nervous system through large myelinated afferant nerve fibers exerted a modulating influence over impulses arriving later via slower-paced "A-delta and C fibers". Later, a so-called "Gate Control Hypothesis" was developed and this hypothesis is that pain relief following peripheral nerve stimulation is due to the inhibition of the small myelinated or unmyelinated fibers by electrically activating the large myelinated fibers. Still later, demonstrated relief of trigeminal neuralgia with implanted electrodes in the region of the trigeminal ganglion was shown.
Work in electrically stimulating sensory fibers of the spinal cord to suppress pain has resulted in the clinical use of implanted dorsal column stimulators (DCS). Following this, in 1967, Dr. Sweet at the Massachusetts General Hospital developed a transcutaneous nerve stimulator (TNS) as a means for screening DCS implant candidates. The TNS proved effective as a noninvasive, non-destructive modality for suppressing pain, and it was therefore developed as an independent modality. Dr. Burton at Temple University and Dr. Long at the University of Minnesota have reported that the TNS technique holds great promise, if problems of size, weight, electrode contact, and the unpleasant noxious response at the electrodes, can be resolved.
As can be seen from the foregoing, electrical signals utilizing a multitude of various waveforms within a specified frequency spectrum have been suggested and/or used to excite peripheral nerves to reduce or eliminate pain transmission to the brain. In addition, many different techniques have been attempted for the purpose of eliminating, or at least decreasing, the concurrent noxious sensations produced by the stimulating waveforms.
The techniques suggested have ranged in complexity from simple adjustments of rate, frequency and voltage to elaborate and complicated electronic circuits. However, none of the prior art electrical stimulator techniques or equipment have successfully solved all of the problems in this area and, more particularly, have not solved the noxious sensation problem.